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C B Krimbas

Publications and source records attributed to C B Krimbas.

At least 19 recordsLinked to original sources
PubMed1993

The phylogeny of nine species of the Drosophila obscura group inferred by the banding homologies of the chromosomal regions. IV. Element C.

Homologies of the sections of the polytene chromosomes of element C, among several species of the obscura group of the genus Drosophila, were established according to the similarity of their banding patterns. The information gathered was used to construct an unrooted phylogenetic tree based on qualitative criteria. This tree is compared to three other similar trees derived from independent information provided by the study of chromosomal elements B, D and E. The general congruence of the patterns of these trees proves the well-foundedness of this approach. A single exception to this congruence is discussed. Finally a consensus tree, encapsulating information from all chromosomal elements, is presented and its topology is compared to those derived from electrophoretic data.

Animals↗
PubMed1993

Studies of the species barrier between Drosophila subobscura and D. madeirensis. III. How universal are the rules of speciation?

The prevalence of Haldane's rule and the large effect of the X chromosome are examined by analysing the genetics of seven abnormal characters in interspecies hybrids between D. subobscura and D. madeirensis. In two cases Haldane's rule is not obeyed (viability and abnormality of the head). In all characters except the abnormal abdominal tergites, an important effect of the X chromosome is observed. There is an asymmetry in the importance of the effect of the X chromosome. The X of D. madeirensis origin induces abnormality mostly in a mixed background. The Y chromosome plays an important role in determining male sterility.

Abdomen↗
PubMed1992

The phylogeny of nine species of the Drosophila obscura group inferred by the banding homologies of chromosomal regions. III. Element D.

The phylogenetic relationships among nine species belonging to the obscura group of the genus Drosophila were deduced, based on similarities of the banding pattern of their polytene chromosomal element D. These similarities were inferred by the comparison of chromosomal photomaps. The phylogenetic reconstruction was the most parsimonious based on seriation by overlapping inversions and on the principle of conservation/disassociation of nearby located segments. The gene sequences of element D for all species studied were relatively easy to recognize in terms of the map of D. obscura, already found to occupy a relative central position in this group. Thus, three clusters of closely related species could be identified: obscura (D. obscura, D. ambigua, and D. tristis), African (D. kitumensis and D. microlabis), and subobscura (D. subobscura, D. madeirensis and D. guanche), with D. subsilvestris standing apart. The results are in agreement with those from the previously studied elements B and E, but element D was found to be much more conclusive concerning the links among the different clusters. Thus, it is inferred that D. guanche occupies an intermediate position between the other two species of its own cluster and all the others. The gene arrangement of D. obscura, directly related to those of the other species, has been identified. In the phylogenetic tree proposed, both the African cluster and D. subsilvestris derive from a hypothetical gene arrangement, intermediate in the pathway between the subobscura and obscura clusters.

Animals↗
PubMed1991

Studies of the species barrier between Drosophila subobscura and D. madeirensis. I. The genetics of male hybrid sterility.

The genetics of hybrid male sterility between Drosophila subobscura and D. madeirensis were studied with the help of 20 markers in backcross males. A major effect resides in the sex chromosomes: backcross males with the X and Y of different origin (mad X-sub Y or sub X-mad Y) have very small and empty testes. In compatible combinations testes are of normal size but males may be sterile or fertile depending on the genetic constitution of their autosomes. Six autosomal factors affecting hybrid male fertility could be postulated. This estimation is based on the assumption of the absence of interaction between viability and fertility. The presence and the mode of such interaction may modify the number of sterility factors.

Animals↗
PubMed1991

Studies of the species barrier between Drosophila madeirensis and Drosophila subobscura. II. Genetic analysis of developmental incompatibilities in hybrids.

The genetic analysis of two abnormal characters, extra sex combs and abnormal head shape in hybrids between Drosophila madeirensis and Drosophila subobscura, revealed a major effect of the X chromosome in both cases. Autosomes also play a role in determining these abnormalities, the E chromosome in case of extra sex combs, the E and O chromosomes in case of abnormal head shape. Autosomes do not cause the two abnormal characters, without interacting with the X chromosome.

Animals↗
PubMed1991

The phylogeny of nine species of the Drosophila obscura group inferred by the banding homologies of chromosomal regions. I. Element B.

The phylogenetic relationships among nine Drosophila species belonging to the obscura group were investigated by establishing the segments displaying banding homologies in their element B (equivalent to the U element of D. subobscura). The phylogenetic ordering of the species was accomplished using overlapping inversions. Two African species, D. kitumensis and D. microlabis, were investigated. These species are homosequential for their element B gene arrangement but differ from that of D. obscura by several rearrangements. Drosophila obscura seems to be most closely related to D. subsilvestris, from which the respective element B gene arrangements differ at least by six inversions. Three species, D. obscura, D. ambigua, and D. tristis, are closely related and form a cluster. Drosophila obscura displays an element B polymorphism for a pericentric inversion for which D. ambigua is fixed for one gene arrangement and D. tristis for the other. Both D. ambigua and D. tristis share a short distal inversion in the small arm of the chromosome, and differ in this respect from D. obscura. Drosophila madeirensis, D. guanche, and D. subobscura all share the same element B gene arrangement, which is acrocentric, but metacentric in all the other species mentioned. It was found that the gene arrangements of the species from the obscura cluster seem to occupy an intermediate position between those of the species of the D. subobscura cluster and those of the African one. The data reported generally are in good agreement with information provided in the literature.

Animals↗
PubMed1990

Evolution of the obscura group Drosophila species. III. Phylogenetic relationships in the subobscura cluster based on homologies of chromosome A.

The Drosophila subobscura cluster comprises D. subobscura, D. madeirensis and D. guanche, species closely related to some interspecific crosses are possible. This paper clarifies definitively the homologies of the segments of the sex chromosome A (= X) among these species and thus permits a phylogenetic seriation of them. This seriation is identical to the one suggested by the study of chromosome O and concordant with similar data for the remaining three rod autosomes (J, U and E), which, however, do not provide qualitative evidence on this subject.

Animals↗
PubMed1990

The phylogeny of nine species of the Drosophila obscura group inferred by the banding homologies of chromosomal regions. II. Element E.

The phylogenetic relationships among nine species of Drosophila belonging to the obscura group were investigated by establishing (according to their banding similarities) the homologous chromosome segments of element E (equivalent to chromosome O of D. subobscura). The phylogenetic relationships were based on the existence of segments in different triads of species, which could only be produced by overlapping inversions. This permitted the ordering of the species belonging to each triad. Drosophila obscura, D. ambigua and D. tristis were found to be very closely related and thus forming a cluster in which D. ambigua occupies an intermediate position between the other two species. Drosophila obscura seems to be the species more directly linked to three other separate lineages, that of D. subsilvestris, the two African species (D. microlabis and D. kitumensis), and the subobscura cluster. The species from this last cluster may be ordered as follows: D. subobscura-D. madeirensis-D. guanche. It is not clear which species of this triad is the direct link to D. obscura. These results completely agree with those produced in an independent study, where element B was considered for the same nine species. Furthermore, the present study clarifies some ambiguities concerning the phylogenetic relationships which remained obscure due to the conservative nature of chromosome B.

Animals↗
PubMed1987

Non-random associations between Lap and Pept-1 loci and gene arrangements of chromosome O in D. subobscura--experiments in laboratory populations.

In this paper the well-known non-random associations between Lap and Pept-1 loci and gene arrangements of chromosome O are studied in laboratory populations of D. subobscura. An increase of the frequency of the allele Lap1.00, towards an equilibrium point (0.70), was found to be associated with an increase of the gene arrangement O3+4. This is an accordance to the associations found in natural populations. On the contrary no such an increase was observed in populations polymorphic for Lap and Pept-1 loci but homokaryotypic for gene arrangement O3+4+8 differing in the initial allele frequencies at these loci. Although epistatic selection cannot be completely ruled out, our results are better explained under the assumption of neutrality.

Alleles↗
PubMed1983

Isozyme variation and heterozygosity in Pinus halepensis L.

The genetic polymorphism of a population of Pinus halepensis was studied using 12 electrophoretically detectable enzyme systems encoded by 7 monomorphic and 10 polymorphic loci. An estimation of population parameters revealed a relatively high average heterozygosity (H = 0.179). The total variation present in the population was partitioned into a high amount of genetic variation within groups, with only 1.3-4.4% of the total variation resulting from genic differences among groups.

Electrophoresis, Starch Gel↗
PubMed1981

The genetics of Drosophila subobscura populations. XVII. Further genic heterogeneity within electromorphs by urea denaturation and the effect of the increased genic variability on linkage disequilibrium studies.

Urea denaturation of allozymes was used to provide finer resolution of allelic states within classes of different electrophoretic mobility. This method gives perfectly repeatable results. About 170 isogenic strains for the O chromosome of Drosophila subobscura, derived from two natural populations, were constructed. Their gene arrangements were studied, as well as eight polymorphic genes located on the O chromosome (Est-5, Odh, Ao, ME, Xdh, Lap, Pept-1 and Acph). Crosses performed indicate that differences in urea sensitivity are genetically controlled by the same genes that control electrophoretic mobility. Twice as many alleles have been detected in comparison to the usual electrophoretic method. However, the effective number of alleles did not increase considerably. Studies of linkage disequilibria, by taking into account the finer resolution of allelic states, gave results nearly identical with those obtained in studies where the usual electrophoretic method was used. Although the power of the test is diminished, the absence of genic associations seems to indicate that there are no hidden linkage disequilibria in electrophoretic studies (because of consolidation effects of real alleles into few electromorph classes). The paucity of linkage disequilibria would indicate that there are no epistatic interactions such as those suggested in the model of FRANKLIN and LEWONTIN (1970).

Alleles↗
PubMed1979

The genetics of Drosophila subobscura populations. IX. Studies on linkage disequilibrium in four natural populations.

Gametic frequencies were obtained in four natural populations of D. sub-obscura by extracting wild chromosomes and subsequently analyzing them for inversions and allozymes. The genes Lap and Pept-1, both located within the same inversions of chromosome O, were found in striking nonrandom associations with them of the same kind and degree in all populations studied. On the contrary, the gene Acph, also located within the previously mentioned inversions, was found in linkage disequilibrium with them only in two populations and of opposite directions. This is also the case for the genes Est-9 and Hk, both located within chromosome E inversions. While the gene Est-9 was in strong linkage disequilibrium with the inversions, of the same kind and degree in all populations studied, Hk was found to be in linkage equilibrium. Allele frequencies for the 29 genes studied do not show geographical variation except for the genes Lap, Pept-1 and Est-9, the ones found in linkage disequilibria with the geographically varying gene arrangements. Although mechanical or historical explanations for these equilibria cannot be ruled out, these data cannot be explained satisfactorily by the "middle gene explanation," which states that loci displaying such linkage disequilibria are the ones located near the break points of inversions, while the ones displaying linkage equilibria with them are located in the middle of them. There is no evidence for consistent linkage disequilibria between pairs of loci, except for the closely linked genes of the complex locus, Est-9. This would imply, if it is not a peculiarity of the Est-9 complex, that the linkage disequilibria are found only between very closely linked loci or that, for less closely linked genes, the associations are too weak to be detected by the usual samples sizes.

Alleles↗
PubMed1976

The Lewontin and Krakauer test on quantitative characters.

It is shown that LEWONTIN and KRAKAUER's test could also be applied to quantitative characters that do not show important dominance and epistatic genetic variances. The design of experiments for this purpose and the error of the estimation of F are discussed.

Gene Frequency↗
PubMed1976

Testing the heterogeneity of F values: a suggestion and a correction.

The use of a pair of populations removes the problems posed by a structured phylogeny (pointed out by A. ROBERTSON) and permits the application of the original test of LEWONTIN and KRAKAUER. In the case of 2n populations studied a suggestion is made to use only n pairs in such a way that no population appears in more than one pair. Data on Dacus analyzed this way show that at least two out of six genes studied are or have been selected.

Genetic Techniques↗
PubMed1975

How many genes are selected in populations of Dacus oleae.

Three natural populations of Dacus oleae have been sampled for six electrophoretically detected polymorphic genes. The distribution of the allele frequencies in the different populations were analyzed by the method suggested by Lewontin and Krakauer (1973) (the various in space one) in order to test for selective neutrality. This method, however, which in our case showed that one or more genes are or have been subjected to selection, does not permit estimation of the number of selected loci. An improvement of this method is proposed that perimts a minimum estimation of the selected genes. About a third of them seem to be selected in our material. In our case however, where a cytological analysis is not possible, genes are not differentiated from possible inversions including these genes.

Alcohol Oxidoreductases↗
PubMed1975

The genetics of Drosophila subobscura populations. V. A study of linkage disequilibrium in natural populations between genes and inversions of the E chromosome.

The genetics of Hk and Est-9 complex gene have been studied in Drosophila subobscura. While Hk alleles mendelize normally, Est-9 is a complex locus consisting of several very closely linked genes with active and silent alleles. Both genes are located on chromosome E; a detailed genetic map was constructed with the help of visible markers and inversions. Both Hk and Est-9 are included in or are very near to inversions of the E chromosome. While Hk does not show linkage disequilibrium either with Est-9 or inversions, Est-9 does show disequilibrium in two ways: both with inversions and between different Est-9 genes. All natural populations studied show the same kind of association between Est-9 gene combinations and inversions. It is argued that these results are better explained by selection than by neutrality.

Alleles↗